I make these hide boxes starting from a dollar store plastic basket, then I put on that plaster cast material (you can make it any shape you want), Then I mix whatever my substrate is for example: the Boa hide below is Coconut and some sand for effect.
This is mixed with podge (its like white glue and is totally toxic free and waterproof) then the mixture is applied to the basket ...
And an old one, Its like his security blanket
If you have any questions please ask
Brian